Phase I, using an available electron-scattering theory devised by one of the investigators, and a small, powerful (but relatively inexpensive) treatment planning (TP) system, showed that it was possible to implement an electron TP algorithm that would permit, in clinically acceptable planning times, the execution of fully three-dimensional calculations and, in addition, takes accurate account of body inhomogeneities, a factor of vital importance in facilitating confident and safe use of the highly-advantageous electron modality. The calculations, in the interest of speed, used a somewhat truncated form of the underlying theory; calculation times of order 5 minutes per field were achieved (a time that could be reduced to approximately 1 minute by use of available transputers, etc.) principally because transform methods were extensively employed. In Phase II, the early success will be exploited by (a) refinement and consolidation of existing theories, including the theory underlying Phase I, and (b) employment of the still relatively inexpensive but vastly more powerful and more versatile computers (3D capabilities, parallel processing facilities, etc.) now available, and of advanced computational techniques such as novel transform approaches; the predictions of the developed and implemented theory will be checked (a) by Monte Carlo and (b) experimental studies, as a preliminary to initial testing (by others) with a view to eventual regulatory approval and commercial sale. The need for later addition of photon and brachytherapy TP modules or for insertion of our electron module into general TP codes developed by others, will be taken account of in the design.